Method for producing anhydrous sodium hydrosulphite using sodium formate, formic acid or formic acid ester

ABSTRACT

Anhydrous sodium hydrosulphite is produced by the reaction of sodium formate, formic acid or formic acid ester with sodium hydroxide and sulphur dioxide or sodium bisulphite in an aqueous solution of alcohol, under a reflux of formic acid ester which is boiled off from the reaction solution, wherein the improvement comprises the steps of adding sodium hydroxide to the formic acid ester which is condensed for reflux and returning the resulting mixture to the reaction solution.

United States Patent Yoshikawa et al.

[ METHOD FOR PRODUCING ANHYDROUS SODIUM HYDROSULPIIITE USING SODIUM FORMATE, FORMIC ACID OR FORMIC ACID ESTER [75] Inventors: Yoshio YoshiliawmUshilzu-M achi,

Ibaraki-ken; Takeo Suzumori, Niijuku-Machi, Tokyo-fu, both i I ofJapan [73] Assignee: Mitsubishi Gas Chemical Co., Ltd.,

Tokyo, Japan [22] Filed: Nov. 23, 1973 [2]] Appl. No.: 418,452

[30] Foreign Application Priority Data Nov. 28, 1972 Japan 47-118528 [52] U.S. Cl. 423/515 [51] Int. Cl C01b 17/98 [58] Field of Search 423/515, 516

[451 Mar. 18, 1975 [56] References Cited UNITED STATES PATENTS 3,411,875 11/1968 Yoshikawa et alt 423/515 3,576,598 3/1971 Plentovich et al..... 423/515 3,714,340 1/1973 Fujiwara et a1. 423/515 Primary ExaminerEarl C. Thomas Attorney, Agent, or Firm-Brooks, Haidt & l-laffner [5 7] ABSTRACT Anhydrous sodium hydrosulphite is produced by the reaction of sodium formate, formic acid or formic acid ester with sodium hydroxide and sulphur dioxide or sodium bisulphite in an aqueous solution of alcohol, under a reflux of formic acid ester which is boiled off from the reaction solution, wherein the improvement comprises the steps of adding sodium hydroxide to the formic acid ester which is condensed for reflux and returning the resulting mixture to the reaction solution.

2 Claims, 1 Drawing Figure METHOD FOR PRODUCING ANHYDROUS SODIUM HYDROSULPHITE USING SODIUM FORMATE, FORMIC ACID OR FORMIC ACID ESTER BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relatesto a method for producing anhydrous sodium hydrosulphite by the reaction ofsodium formate, formic acid or formic acid ester with sodium hydroxide and sulphur dioxide or sodium bisulphite in an aqueous solution of alcohol.

2. Description of the Prior Art As a commercial method for producing anhydrous sodium hydrosulphite by using sodium formate as starting material, there is known a method which comprises adding an aqueous sodium hydroxide solution and methanol containing sulphur dioxide while adjusting the pH of the reaction solution within an appropriate range. There has been also proposed a method for producing anhydrous sodium hydrosulphite from the above mentioned raw materials, in which a formic acid ester is produced as a by-product and the ester is boiled off from the reaction solution together with carbon dioxide produced as shown below, and thereby the yield is reduced.

HCOONa 280 NaOH Na S O CO H O In such method, therefore, the formic acid ester is condensed by cooling it below its boiling point, preferably below C in the case of methyl ester, and subse quently returned to the reaction solution.'

SUMMARY OF THE lNVENTlON According to the present invention, there is provided a method for producing anhydrous sodium hydrosulphite by the reaction of sodium formate, formic acid or formic acid ester with sodium hydroxide and sulphur dioxide or sodium bisulphite in an aqueous solution of alcohol under reflux of formic acid ester which is boiled off from the reaction solution, wherein the improvement comprises the steps of adding sodium hydroxide to the formic acid ester which is condensed for reflux and returning the resulting mixture to the reaction solution.

BRlEF DESCRIPTION OF THE DRAWING The attached drawing shows a flow sheet of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In our opinion the reaction of sodium hydrosulphite formation is considered to proceed as follows:

HCOONa H O S0 HCOOH NaHSO NaOH so NaHSO Sodium formate is a starting material for forming formic acid and sodium bisulphite as shown in formula (1). And the sodium formate which does not take part in the reaction serves as a buffer to stabilize the pH of the reaction solution to prevent the decomposition of the hydrosulphite produced. Therefore the concentration of sodium formate in the reaction solution should be kept sufficiently high to stabilize the pH of the reaction solution. The preferable pH of the reaction solution ranges from 4 to 6.

Formic acid formed by reaction l produces sodium hydrosulphite by reaction (3 and furthermore produces formic acid ester as by-product according to the following formula:

HCOOH MeOH HCOOMe H 0 The formic acid ester thus formed has a low boiling point and is so volatile that it tends to be lost.

Consequently, there has been disclosed a method wherein the formic acid ester is condensed by cooling below its boiling point and is subsequently returned to the reaction solution to participate in the reaction as mentioned above. However, because most of the condensed formic acid ester is vaporized again before taking part in the reaction, the capacity of the vapour condenser should be designed inevitably to be large. In addition, it is difficult to utilize the formic acid ester sufficiently for the production of the sodium hydrosulphite.

According to the present invention, the condensed formic acid ester is once introduced into a small vessel; and a part of, or all of sodium hydroxide used in the reaction is introduced into the condensed formic acid ester, and the resulting mixture is allowed to react according to the equation as shown below, and returned to the reaction solution.

HCOOMe NaOH HCOONa MeOH According to the above mentioned procedure of the present invention, the capacity of the vapour condenser can be reduced to from one third to a half of that in the conventional method, and moreover, the yield and the purity of the product are markedly improved. The refluxing liquid enters into the reactor in a form of sodium formate and methanol as the result of the reaction (5). and lowering of the concentration of sodium formate caused by formation of water according to the formula (3) can be avoided and furthermore the amount of sodium formate to be charged as raw material into the reactor can be reduced.

Reduction of the duty of the vapour condenser results in reduction of utilities such as steam, electricity, etc., and remarkable commercial advantage can be achieved.

In the case of using formic acid or formic acid ester as raw material, these materials may be added to the reaction solution at a rate corresponding to the rate of the production of the hydrosulphite, so as to maintain an optimum pH during the reaction.

Also in this case sodium formate can behave as a buffer in the reaction solution to facilitate control of the pH and therefore it is quite preferable that an appropriate amount of sodium formate be present in the initial reaction solution.

3 4 In the method of the present i e t on. the reaction ature was lZe ptat82 C for 2 hours under a pressure of may be effected at atmospheric or superatmospheric l Kg/cm' gauge so as to complete the reaction.- pressure. After the reaction was completed, the same treat- The following examples are given for illustrating the ment as described in Example 1 was carried out, The present invention, and are by no means to be construed 5 yield of the final product was 1 19 parts with a purity of as limitation thereof. 93.2 percent. The product is not powdery and its parti- EXAMPLE 1 cle slze dlstrlbutlon ls shown ln Table 2 below.

Referring to the drawing, 80 parts of sodium formate, Table 2 40 parts of water and 120 parts of methanol were Particle M49 149% 105:4 74 62 62 charged into the reactor 1 through conduit a, and the Shem) resulting slurry was heated up to 74 C under atmospheric pressure. After the start of reflux, a solution in zi g 2 73 23 3 l which 100 parts of sulphur dioxide was absorbed in 305 parts of methanol was uniformly added to the reactor 15. Oh h other h d h the aqueous di h 1 under stirr ng in 2 hours- The p r Containing droxide solution was directly added to the reactor 1, mic acid ester was condensed by the water cooling conh i ld f h fi l product was 1 12 parts with denser 2 and the vapour condenser 3 and the conm f 92 5 t,

densed liquid was led to the mixing vessel 4. The gas which was not condensed was exhausted through the EXAMPLE 3 ductc The condensed liquid was mixed and allowed 80 rt f etha l and 35 parts of water were to react with an aqueous sodium hydroxide solution inh d i t th r t r 1, The resulting slurry was troduced through conduitb, and then returned to the h t d up to 82 C, d h i pressure was dreactor 1. The aqueous sodium hydroxide solution was j t d t 1 Kg/cm gauge. The solution in which 100 prepared by disso g 33 par of Sodium y r id in parts of sulphur dioxide was absorbed in 305 parts of 45 parts of water and was uniformly added to the eonmethanol was added dropwise to the reactor 1 under densed liquid in 2 hours. stirring in 2 hours.

The reaction Solution as kept at ts boiling Po nt Simultaneously with addition of the methanol soluunder stirring for an additional 3 hours, d en ti'on containing sulphur dioxide, 76 parts ofmethyl forcooled to 60 C. l mate and the aqueous sodium hydroxide solution pre- The hydrosulphite produced was separated in the pared by dissolving 80 parts of sodium hdyroxide in 70 form of its anhydrous salt from the alcohol-water soluparts of water were dropwise charged uniformly tion by filtration, washed with methanol and dried through the mixing vessel 4 into the reactor during 80 under vacuum. The yield of the final produce was 109 minutes.

parts with a purity of 93.5 percent. The product was Methyl formate boiled off from the reaction solution not powdery. The particle size distribution is shown in was condensed and led to the mixing vessel.

Table 1 below.

Table 1 Particle 250 250-177 177-149 149-105 105-74 74-62 62 size(p.)

Distribution 65 12 5 13 2 3 0 On the other hand when the aqueous sodium hylution containing sulphur dioxide, the reaction temper droxide was not mixed with the condensed liquid and ature was kept at 82 C for 2 hours under pressure of other procedures were conducted in a way similar to l Kg/cm gauge so as to complete the reaction.

those as mentioned above, the yield of the final product was 100 parts with a purity of 91.5 percent.

After the reaction was completed, the same treatment as described in Example 1 was carried out. The yield of the final product was 121 parts with a purity of EXAMPLE 2 92.5 percent. The product is not powdery and its parti- 73 parts of sodium formate, 45 parts of water and cle size distribution is shown in,Table 3 below. 1 10 parts of methanol were charged into the reactor 1. Table 3 The resulting slurry was heated up to77 C, and the re- After completion of the addition of the methanol soaction pressure was adjusted to 0.6Kg/cm gauge. A so- Particle 149 149405 0544' 74 62 62 lution in which 98.7 parts of sulphur dioxide was absize(;t)

sorbed in 305 parts of methanol was added dropwise to the reactor 1 with stirring in 2 hours. 4 v 27 H 3 Simultaneously with addition of the methanol solu- I tion containing sulphur dioxide, the aqueous sodium On the other hand, when the aqueous sodium hyhydroxide solution prepared by dissolving 37 parts of droxide solution was directly added to the reactor 1, sodium hydroxide in 40 par of wat r was charged the yield of the final product was 109 parts with a pudropwise through the mixing vessel 4 into the reactor my of 91 percent. 1 during 2 hours. We claim:

After completion of the addition of the methanol so- 1. In a method for producing anhydrous sodium hylution containing sulphur dioxide, the reaction temperdrosulphite by the reaction of sodium formate, formic flux and returning the resulting mixture to the reaction solution.

2. A method as claimed in claim 1, wherein the alcohol is methanol and the formic acid ester is methyl formate. 

1. IN A METHOD FOR PRODUCING ANHYDROUS SODIUM HYDROSULPH- ITE BY THE REACTION OF SODIUM FORMATE, FORMIC ACID OR FORMIC ACID ESTER WITH SODIUM HYDROXIDE AND SULPHUR DIOXIDE OR SODIUM BISULPHITE IN AN AQUEOUS SOLUTION OF ALCOHOL, UNDER REFLUX OF FORMIC ACID ESTER WHICH IS BOILED OFF FROM THE REACTION SOLUTION, THE IMPROVEMENT COMPRISING THE STEPS OF ADDING SODIUM HYDROXIDE TO FORMIC ACID ESTER WHICH IS CONDENSED FOR REFLUX AND RETURNING THE RESULTING MIXTURE TO THE REACTION SOLUTION.
 2. A method as claimed in claim 1, wherein the alcohol is methanol and the formic acid ester is methyl formate. 